The monastery’s greenhouse is located in the southwestern portion of the Map where you can do gardening whenever you’re exploring. There’s a quest that will require you to visit it and talk to the Greenhouse Keeper so you won’t miss this location. When you talk to the Keeper, you’ll have three options:
* Plant
* Cultivate
* Harvest

Plant

Every week, you can plant seeds from your inventory. You can get seeds from random pick up locations around the monastery, Amiibo Gazebo, quest rewards, and later on, purchase them from merchants. The items you can harvest from gardening may range from food ingredients, tea leaves (for Tea Parties), flowers, and even rare items that can give you permanent stat boosts. Flowers are perfect gifts to increase another character’s affinity towards you; some characters may even decorate their rooms with flowers you gave them.

The number of seeds you can plant will depend on your Professor Level. You’ll start off with the Ability to plant one type of seed. As your Professor Level goes up, the number of seeds you can plant per session also increases. At Professor Level A+, you can plant up to 5 seeds.

Cultivate

This option allows you to use available techniques to improve your plants’ growth. This is also affected by your professor level. As it goes up, more cultivation options will be unlocked. It is strongly recommended to select the best cultivation option you have access to, to ensure that you get better yield. You can only select one Cultivation method per session.

Harvest

Select this option to harvest the crop that you planted from the last gardening session. The amount of items you’ll get will depend on the type of seeds you planted and the selected cultivation method last time. After harvesting your crops, you can immediately plant again.

Harvested Items

In this section, we will list down what items you can get from seeds you plant. Each seed has a chance to randomly produce up to 10 different items. Planting the same seeds increases the chances of you getting more of what you can possibly get from the seeds. Items in bold and colored blue are special consumables that permanently increases the stats of the unit you used it on. Credits to IGN's article for helping us fill the information we're missing.